Thesis EDM

7/31/2019 Thesis EDM

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A THESIS SUBMITTED IN PARTIAL FULFILMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

Master of Technology

In

Mechanical Engineering

By

SHAILESH KUMAR DEWANGAN

Department of Mechanical Engineering

National Institute of Technology

Rourkela (India)

2010



Experimental Investigation of Machining Parameters for EDM

Using U-shaped Electrode of AISI P20 Tool Steel

A THESIS SUBMITTED IN PARTIAL FULFILMENT

OF THE REQUIREMENTS FOR THE DEGREE OF

Master of Technology

In

Mechanical Engineering

By

SHAILESH KUMAR DEWANGAN

UNDER THE GUIDANCE OF

Dr. C.K. BISWAS

Department of Mechanical Engineering


Rourkela (India)



This is to certify that t

MACHINING PARAMET

P20 TOOL STEEL ” subm

fulfillment of the require

Engineering with “Productio

Department of Mechanical En

It is an authentic work carried

knowledge, the matter embo

University/Institute for awar

Date


Rourkela (India)

CERTIFICATE

hesis entitled, “EXPERIMENTAL IN

RS FOR EDM USING U-SHAPED EL

itted by Mr. SHAILESH KUMAR DE

ents for the award of Master of Tech

n Engineering” Specialization during sess

gineering National Institute of Technology,

out by him under my supervision and guida

died in this thesis has not been sub

d of any Degree or Diploma.

Department of Me

National institute of

i

ESTIGATION OF

CTRODE OF AISI

ANGAN in partial

nology in Mechanical

ion 2009-2010 in the

ourkela.

nce. To the best of my

itted to any other

Dr. C. K. Biswas

Associate Professor

chanical Engineering

technology, Rourkela



ii

Acknowledgement

I express my deep sense of gratitude and indebtedness to my thesis supervisor Dr. C. K.

Biswas, Associate Professor, Department of Mechanical Engineering for providing precious

guidance, inspiring discussions and constant supervision throughout the course of this work. His

timely help, constructive criticism, and conscientious efforts made it possible to present the work

contained in this thesis.

I express my sincere thanks to Mr. Mohan Kumar Pradhan, Research Scholar and Mr. K.

Nayak, Technical Assistance in Production Engineering lab. I am grateful to Prof. R. K. Sahoo,

Head of the Department of Mechanical Engineering for providing me the necessary facilities in

the department. I express my sincere gratitude to Prof. S.S. Mahapatra, coordinator of M.E.

course for his timely help during the course of work. I am also thankful to all the staff members

of the department of Mechanical Engineering and to all my well wishers for their inspiration and

help. And also to thanks my classmate’s Jaikishan Pandri, A Prabhkar and Banu Kiran during the

help my project.

I feel pleased and privileged to fulfill my parent’s ambition and I am greatly indebted to them

for bearing the inconvenience during my M Tech. course.

Date Shailesh kumar Dewangan

Roll No. 208ME202



iii

ABSTRACT

The correct selection of manufacturing conditions is one of the most important aspects to

take into consideration in the majority of manufacturing processes and, particularly, in processes

related to Electrical Discharge Machining (EDM). It is a capable of machining geometrically

complex or hard material components, that are precise and difficult-to-machine such as heat

treated tool steels, composites, super alloys, ceramics, carbides, heat resistant steels etc. being

widely used in die and mold making industries, aerospace, aeronautics and nuclear industries.

AISI P20 Plastic mould steel that is usually supplied in a hardened and tempered condition.

Good machinability, better polishability, it has a grooving rang of application in Plastic moulds,

frames for plastic pressure dies, hydro forming tools These steel are categorized as difficult to

machine materials, posses greater strength and toughness are usually known to create major

challenges during conventional and non- conventional machining. The Electric discharge

machining process is finding out the effect of machining parameter such as discharge current,

pulse on time and diameter of tool of AISI P20 tool steel material. Using U-shaped cu tool with

internal flushing. A well-designed experimental scheme was used to reduce the total number of

experiments. Parts of the experiment were conducted with the L18 orthogonal array based on the

Taguchi method. Moreover, the signal-to-noise ratios associated with the observed values in the

experiments were determined by which factor is most affected by the Responses of Material

Removal Rate (MRR), Tool Wear Rate (TWR) and over cut (OC).



iv

Contents

Page no.

CERTIFICATE i

ACKNOWLEDGEMENT Ii

ABSTRACT Iii

CONTENTS iv

LIST OF FIGURES vii

LIST OF TABLES viii

CHAPTER-1 INTRODUCTION 1

1.1 Background of Electric discharge machine (EDM) 1

1.2 Introduction of EDM 2

1.3 Principle of EDM 2

1.4 Types of EDM 4

1.4.1 Die-sinking 4

1.4.2 Wire cut EDM 5

1.5 Important parameters of EDM 6

1.6 Characteristics of EDM 7

1.7 Dielectric fluid 8

1.8 Flushing method 8

1.9 Tool Material 91.10 Design variable 10

1.11 Workpiece material 11

1.12 Application of EDM 11

1.13 Advantages of EDM 12

1.14 Limitation of EDM 13



v

CHAPTER- 2 LITERATURE SURVEY 14

2.1 Workpiece and tool material of EDM 142.2 EDM with tubular electrode 20

2.3 EDM tool design 21

2.4 Effect of multiple discharges of EDM 22

2.5 EDM with CNC 23

2.6 Objective of the present work 26

CHAPTER -3 EXPERIMENTAL WORKS 27

3.1 Experimental set up 27

3.1.1 Dielectric reservoir, pump and circulation system 28

3.1.2 Power generator and control unit 28

3.1.3 Working tank with work holding device 29

3.1.4 X-Y table accommodating the working table 29

3.1.5 The tool holder 29

3.1.6 The servo system to feed the tool. 303.2 Section of the work piece 30

3.3 Tool design 32

3.4 Flow chart of experiment 34

3.5 Mechanism of Material removal rate 35

3.5.1 Evaluation of MRR 35

3.6 Mechanism of Tool wears 36

3.6.1 Evaluation of TWR 36

3.7 Mechanism of over cut 36

3.7.1 Evaluation of over cut 37

3.8 Taguchi design 37

3.9 Taguchi design experiments in MINITAB 37

3.10 Conduct of Experiment 38

3.11 Design matrix and observation table 39



vi

3.12 Conclusion 40

CHAPTER -4 RESULTS AND DISCUSSION 41

4.1 Response Table 41

4.2 Influences on MRR 42

4.2.1 Model Analysis of MRR 45

4.3 Influences of TWR 46

4.3.1 Model Analysis of TWR 49

4.4 Influences of Over cut 50

4.4.1 Model Analysis of OC 53

CHAPTER - 5 CONCLUSIONS 55

CHAPTER – 6 APPENDIX 56

CHAPTER- 7 REFERENCES 61

CHAPTER- 8 BIBLIOGRAPHY 68



vii

LIST OF FIGURES

Figure no. Title Page no.

1.1 Set up of Electric discharge machining 3

1.2 Working principle of EDM process 4

1.3 Die sinking & wire cut EDM Process 6

1.4 Flushing of U-tube Cu electrode 9

2.1 Graph between interactive effect of Sic and Current on MRR 15

2.2 Multi Response optimization for Max. MRR and Min.TWR 15

2.3 MRR and surface roughness with pulse duration graph 16

2.4 Design of Cu ring tool shaped B-EDM 18

2.5 Experimental set-up 20

2.6 Solid model of workpiece and interference between work and tool 23

2.7 Compensation for wear during scanning of a layer 25

3.1 Dielectric reservoirs 28

3.2 Control unit of EDM machine 29

3.3 Tool holder with Workpiece and tool 29

3.4 P20 Workpiece and Cu U-shaped tool 32

3.5 U - Tube Copper tool design 33

3.6 U-shaped Copper tool 33

3.7 Crater formation in EDM process 35

4.1 Main effect plot for MRR 44

4.2 Interaction plot for MRR 44

4.3 Residual plot for MRR 46

4.4 Main effect plot for TWR 48

4.5 Interaction plot for TWR 48

4.6 Residual plot for TWR 50

4.7 Main effect plot for over cut 52

4.8 Interaction plot for over cut 52

4.9 Residual plot for over cut 54

5.1 Die Sinker EDM Model: PS 50ZNC 56



viii

5.2 Electronic Balance weight machine 57

5.3 Tool maker microscope 57



ix

LIST OF TABLES

Table no. Title Page no.

1.1 Specification on EDM 7

3.1 Composition of AISI P-20 tool steel material 30

3.2 AISI P20 Steel categories 31

3.3 Mechanical properties of P20 steel 31

3.4 Thermal properties of P20 steel 31

3.5 Machining parameters and their level 38

3.6 Design matrix and observation Table 39

4.1 Response table 41

4.2 ANOVA for S/N Ratios (MRR) 42

4.3 Response for S/N Ratios Larger is better (MRR) 43

4.4 Estimation model for Coefficient (MRR) 45

4.5 ANOVA for S/N Ratios (TWR) 47

4.6 Response for S/N Ratios smaller is better (TWR) 47

4.7 Estimation model for Coefficient (TWR) 494.8 ANOVA for S/N Ratios (over cut) 51

4.9 Response for S/N Ratios smaller is better (over cut) 51

4.10 Estimation model for Coefficient (over cut) 53



Page 1

Chapter 1

1.1 Background of EDM

The history of EDM Machining Techniques goes as far back as the 1770s when it was

discovered by an English Scientist. However, Electrical Discharge Machining was not fully

taken advantage of until 1943 when Russian scientists learned how the erosive effects of the

technique could be controlled and used for machining purposes.

When it was originally observed by Joseph Priestly in 1770, EDM Machining was very

imprecise and riddled with failures. Commercially developed in the mid 1970s, wire EDM began

to be a viable technique that helped shape the metal working industry we see today. In the mid

1980s.The EDM techniques were transferred to a machine tool. This migration made EDM more

widely available and appealing over traditional machining processes.

The new concept of manufacturing uses non-conventional energy sources like sound,

light, mechanical, chemical, electrical, electrons and ions. With the industrial and technological

growth, development of harder and difficult to machine materials, which find wide application in

aerospace, nuclear engineering and other industries owing to their high strength to weight ratio,

hardness and heat resistance qualities has been witnessed. New developments in the field of

material science have led to new engineering metallic materials, composite materials and high

tech ceramics having good mechanical properties and thermal characteristics as well as sufficient

electrical conductivity so that they can readily be machined by spark erosion. Non-traditional

machining has grown out of the need to machine these exotic materials. The machining

processes are non-traditional in the sense that they do not employ traditional tools for metal

removal and instead they directly use other forms of energy. The problems of high complexity in

shape, size and higher demand for product accuracy and surface finish can be solved through

non-traditional methods. Currently, non-traditional processes possess virtually unlimited



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capabilities except for volumetric material removal rates, for which great advances have been

made in the past few years to increase the material removal rates. As removal rate increases, the

cost effectiveness of operations also increase, stimulating ever greater uses of nontraditional

process. The Electrical Discharge Machining process is employed widely for making tools, dies

and other precision parts.

EDM has been replacing drilling, milling, grinding and other traditional machining

operations and is now a well established machining option in many manufacturing industries

throughout the world. And is capable of machining geometrically complex or hard material

components, that are precise and difficult-to-machine such as heat treated tool steels, composites,

super alloys, ceramics, carbides, heat resistant steels etc. being widely used in die and mold

making industries, aerospace, aeronautics and nuclear industries. Electric Discharge Machining

has also made its presence felt in the new fields such as sports, medical and surgical,

instruments, optical, including automotive R&D areas.

1.2 Introduction of EDM -

Electro Discharge Machining (EDM) is an electro-thermal non-traditional machining

Process, where electrical energy is used to generate electrical spark and material removal mainly

occurs due to thermal energy of the spark.

EDM is mainly used to machine difficult-to-machine materials and high strength

temperature resistant alloys. EDM can be used to machine difficult geometries in small batches

or even on job-shop basis. Work material to be machined by EDM has to be electrically

conductive.

1.3 Principle of EDM –

In this process the metal is removing from the work piece due to erosion case by rapidly

recurring spark discharge taking place between the tool and work piece. Show the mechanical set

up and electrical set up and electrical circuit for electro discharge machining. A thin gap about

0.025mm is maintained between the tool and work piece by a servo system shown in fig 1.1.

Both tool and work piece are submerged in a dielectric fluid .Kerosene/EDM oil/deionized water



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is very common type of liquid dielectric although gaseous dielectrics are also used in certain

cases.

Figure1. 1 Set up of Electric discharge machining

This fig.1.1 is shown the electric setup of the Electric discharge machining. The tool is

mead cathode and work piece is anode. When the voltage across the gap becomes sufficiently

high it discharges through the gap in the form of the spark in interval of from 10 of micro

seconds. And positive ions and electrons are accelerated, producing a discharge channel that

becomes conductive. It is just at this point when the spark jumps causing collisions between ions

and electrons and creating a channel of plasma. A sudden drop of the electric resistance of the

previous channel allows that current density reaches very high values producing an increase of

ionization and the creation of a powerful magnetic field. The moment spark occurs sufficientlypressure developed between work and tool as a result of which a very high temperature is

reached and at such high pressure and temperature that some metal is melted and eroded.

Such localized extreme rise in temperature leads to material removal. Material removal

occurs due to instant vaporization of the material as well as due to melting. The molten metal is

not removed completely but only partially



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As the potential difference is withdrawn as shown in Fig. 1.2, the plasma channel is no

longer sustained. As the plasma channel collapse, it generates pressure or shock waves, which

evacuates the molten material forming a crater of removed material around the site of the spark .

Figure1. 2 Working principle of EDM process

1.4 Types of EDM –

Basically, there are two different types of EDM:

1.4.1) Die-sinking

1.4.2) wire-cut.

1.4.1Die-sinking EDM –

In the Sinker EDM Machining process, two metal parts submerged in an insulating liquid

are connected to a source of current which is switched on and off automatically depending on the

parameters set on the controller. When the current is switched on, an electric tension is created

between the two metal parts. If the two parts are brought together to within a fraction of an inch,

the electrical tension is discharged and a spark jumps across. Where it strikes, the metal is heated

up so much that it melts. Sinker EDM, also called cavity type EDM or volume EDM consists of

an electrode and workpiece submerged in an insulating liquid such as, more typically, oil or, less

frequently, other dielectric fluids. The electrode and workpiece are connected to a suitable power

supply. The power supply generates an electrical potential between the two parts. As the

electrode approaches the workpiece, dielectric breakdown occurs in the fluid, forming a plasma

channel, and a small spark jumps.



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These sparks usually strike one at a time because it is very unlikely that different locations

in the inter-electrode space have the identical local electrical characteristics which would enable

a spark to occur simultaneously in all such locations. These sparks happen in huge numbers at

seemingly random locations between the electrode and the workpiece. As the base metal is

eroded, and the spark gap subsequently increased, the electrode is lowered automatically by the

machine so that the process can continue uninterrupted. Several hundred thousand sparks occur

per second, with the actual duty cycle carefully controlled by the setup parameters.

1.4.2 Wire-cut EDM –

Wire EDM Machining (also known as Spark EDM) is an electro thermal production

process in which a thin single-strand metal wire (usually brass) in conjunction with de-ionized

water (used to conduct electricity) allows the wire to cut through metal by the use of heat from

electrical sparks. a thin single-strand metal wire, usually brass, is fed through the workpiece,

submerged in a tank of dielectric fluid, typically deionized water. Wire-cut EDM is typically

used to cut plates as thick as 300mm and to make punches, tools, and dies from hard metals that

are difficult to machine with other methods.

Wire-cutting EDM is commonly used when low residual stresses are desired, because it

does not require high cutting forces for removal of material. If the energy/power per pulse is

relatively low (as in finishing operations), little change in the mechanical properties of a material

is expected due to these low residual stresses, although material that hasn't been stress-relieved

can distort in the machining process. Due to the inherent properties of the process, wire EDM

can easily machine complex parts and precision components out of hard conductive materials.



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Figure1. 3 Die sinking & wire cut EDM Process

1.5 Important parameters of EDM

(a)

Spark On-time (pulse time or Ton): The duration of time (µs) the current is allowed to

flow per cycle. Material removal is directly proportional to the amount of energy applied

during this on-time. This energy is really controlled by the peak current and the length of

the on-time.

(b) Spark Off-time (pause time or Toff ): The duration of time (µs) between the sparks

(that is to say, on-time). This time allows the molten material to solidify and to be wash

out of the arc gap. This parameter is to affect the speed and the stability of the cut. Thus,

if the off-time is too short, it will cause sparks to be unstable.

(c) Arc gap (or gap): The Arc gap is distance between the electrode and workpiece during

the process of EDM. It may be called as spark gap. Spark gap can be maintained by servo

system (fig no.-1).

(d) Discharge current (current Ip): Current is measured in amp Allowed to per cycle.

Discharge current is directly proportional to the Material removal rate.

(e) Duty cycle (τ): It is a percentage of the on-time relative to the total cycle time. This

parameter is calculated by dividing the on-time by the total cycle time (on-time pulse off-

time).

τ =

(f) Voltage (V): It is a potential that can be measure by volt it is also effect to the material

removal rate and allowed to per cycle. Voltage is given by in this experiment is 50 V.



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(g) Diameter of electrode (D): It is the electrode of Cu-tube there are two different size of

diameter 4mm and 6mm in this experiment. This tool is used not only as a electrode but

also for internal flushing.

(h)

Over cut – It is a clearance per side between the electrode and the workpiece after the

marching operation.

1.6 Characteristics of EDM

EDM specification by mechanism of process, metal removal rate and other function that

shown in this table no .1

Table1.1 Specification on EDM

Mechanism of process Controlled erosion (melting and evaporation) through aseries of electric spark

Spark gap 0.010- 0.500 mm

Spark frequency 200 – 500 kHz

Peak voltage across the gap 30- 250 V

Metal removal rate (max.) 5000 mm3 /min

Specific power consumption 2-10 W/mm3 /min

Dielectric fluid EDM oil, Kerosene liquid paraffin, silicon oil, deionizedwater etc.

Tool material Copper, Brass, graphite, Ag-W alloys, Cu-W alloys .

MRR/TWR 0.1-10

Materials that can be machined All conducting metals and alloys.

Shapes Microholes, narrow slots, blind cavities

Limitations High specific energy consumption, non conductingmaterials can’t be machined.



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1.7 Dielectric fluid

In EDM, as has been discussed earlier, material removal mainly occurs due to thermal

evaporation and melting. As thermal processing is required to be carried out in absence of

oxygen so that the process can be controlled and oxidation avoided. Oxidation often leads to

poor surface conductivity (electrical) of the work piece hindering further machining. Hence,

dielectric fluid should provide an oxygen free machining environment. Further it should have

enough strong dielectric resistance so that it does not breakdown electrically too easily but at the

same time ionize when electrons collide with its molecule. Moreover, during sparking it should

be thermally resistant as well.

The dielectric fluid has the following functions:

(a)

It helps in initiating discharge by serving as a conducting medium when ionised, and

conveys the spark. It concentrates the energy to a very narrow region.

(b) It helps in quenching the spark, cooling the work, tool electrode and enables arcing to be

prevented.

(c) It carries away the eroded metal along with it.

(d) It acts as a coolant in quenching the sparks.

The electrode wear rate, metal removal rate and other operation characteristics are also

influenced by the dielectric fluid.The dielectric generally fluid used are transformer on silicon oil, EDM oil, kerosene (paraffin

oil) and de-ionized water are used as dielectric fluid in EDM. Tap water cannot be used as it

ionizes too early and thus breakdown due to presence of salts as impurities occur. Dielectric

medium is generally flushed around the spark zone. It is also applied through the tool to achieve

efficient removal of molten material.

In this experiment using the Commercial grade EDM oil (specific gravity= 0.763, freezing

point= 94˚C) was used as dielectric fluid are used it is using as coolant and medium of workpiece

and tool during the process of erosion.

1.8. Flushing method-

Flushing is the most important function in any electrical discharge machining operation.

Flushing is the process of introducing clean filtered dielectric fluid into the spark gap. There are

a number of flushing methods used to remove the metal particles efficiently.



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This experiment is using the internal flushing with the Cu U- shaped tool shown in the fig

no. 1.4.

Figure 1. 4 Flushing of U-tube Cu electrode

1.9. Tool Material-

Tool material should be such that it would not undergo much tool wear when it is impinged

by positive ions. Thus the localized temperature rise has to be less by tailoring or properly

choosing its properties or even when temperature increases, there would be less melting. Further,

the tool should be easily workable as intricate shaped geometric features are machined in EDM.

Thus the basic characteristics of electrode materials are:

1. High electrical conductivity – electrons are cold emitted more easily and there is less bulk

electrical heating.

2.

High thermal conductivity – for the same heat load, the local temperature rise would be

less due to faster heat conducted to the bulk of the tool and thus less tool wear.

3. Higher density – for the same heat load and same tool wear by weight there would be less

volume removal or tool wear and thus less dimensional loss or inaccuracy.

4. High melting point – high melting point leads to less tool wear due to less tool material

melting for the same heat load.

5. Easy manufacturability.



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6. Cost – cheap.

The followings are the different electrode materials which are used commonly in the

industry:

1.

Graphite

2. copper

3. Tellurium copper – 99% Cu + 0.5% tellurium

4. Brass

In this experiment are using the Cu tool U-shaped tool with internal flushing system this

tool material can be eroded by U shaped.

1.10. Design variable-

Design parameter, process parameter and constant parameter are following ones,

Design parameters –

1. Material removal rate.

2. Tool wear rate

3. Over cut (OC)

Machining parameter –

1. Discharge current (Ip)

2. Pulse on time (Ton)

3. Diameter of U-shaped tool

Constant parameter-

1.

Duty cycle

2. Voltage

3. Flushing pressure

4. Polarity



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1.11. Workpiece material-

It is capable of machining geometrically complex or hard material components, that

are precise and difficult-to-machine such as heat treated tool steels, composites, super alloys,

ceramics, carbides, heat resistant steels etc.

There are different types of tool material are using the EDM method. And the tool steel

contains carbon and alloy steels that are particularly well-suited to be made into tools. Their

suitability comes from their distinctive hardness, resistance to abrasion, their ability to hold a

cutting edge, and/or their resistance to deformation at elevated temperatures (red-hardness). Tool

steel is generally used in a heat-treated state. Tool steels are made to a number of grades for

different applications. In general, the edge temperature under expected use is an important

determinant of both composition and required heat treatment. The higher carbon grades are

typically used for such applications as stamping dies, metal cutting tools, etc .

In this experiment are using AISI P-20 plastic mould tool steel material.

1.12 Application of EDM –

1. The EDM process is most widely used by the mould-making tool and die industries, but is

becoming a common method of making prototype and production parts, especially in the

aerospace, automobile and electronics industries in which production quantities are relatively

low.

2. It is used to machine extremely hard materials that are difficult to machine like alloys, tool

steels, tungsten carbides etc.

3. It is used for forging, extrusion, wire drawing, thread cutting.

4. It is used for drilling of curved holes.

5. It is used for internal thread cutting and helical gear cutting.

6. It is used for machining sharp edges and corners that cannot be machined effectively by other

machining processes.



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7. Higher Tolerance limits can be obtained in EDM machining. Hence areas that require higher

surface accuracy use the EDM machining process.

8. Ceramic materials that are difficult to machine can be machined by the EDM machining

process.

9. Electric Discharge Machining has also made its presence felt in the new fields such as sports,

medical and surgical, instruments, optical, including automotive R&D areas.

10. It is a promising technique to meet increasing demands for smaller components usually

highly complicated, multi-functional parts used in the field of micro-electronics.

1.13

Advantages of EDM(a) Any material that is electrically conductive can be cut using the EDM process.

(b) Hardened workpieces can be machined eliminating the deformation caused by heat

treatment.

(c) X, Y, and Z axes movements allow for the programming of complex profiles using simple

electrode.

(d) Complex dies sections and molds can be produced accurately, faster, and at lower costs.

Due to the modern NC control systems on die sinking machines, even more complicated work pieces can be machined.

(e) The high degree of automation and the use of tool and work piece changers allow the

machines to work unattended for overnight or during the weekends

(f) Forces are produced by the EDM-process and that, as already mentioned, flushing and

hydraulic forces may become large for some work piece geometry. The large cutting forces of

the mechanical materials removal processes, however, remain absent.

(g) Thin fragile sections such as webs or fins can be easily machined without deforming the

part.



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1.14 Limitation of EDM –

(a) The need for electrical conductivity – To be able to create discharges, the work piece has

to be electrically conductive. Isolators, like plastics, glass and most ceramics, cannot be

machined by EDM, although some exception like for example diamond is known.

Machining of partial conductors like Si semi-conductors, partially conductive ceramics and

even glass is also possible.

(b) Predictability of the gap - The dimensions of the gap are not always easily predictable,

especially with intricate work piece geometry. In these cases, the flushing conditions and

the contamination state of differ from the specified one. In the case of die-sinking EDM,

the tool wear also contributes to a deviation of the desired work piece geometry and it

could reduce the achievable accuracy. Intermediate measuring of the work piece or some

preliminary tests can often solve the problems.

(c) Low material removal rate- The material removal of the EDM-process is rather low,

especially in the case of die-sinking EDM where the total volume of a cavity has to be

removed by melting and evaporating the metal. With wire-EDM only the outline of the

desired work piece shape has to be machined. Due to the low material removal rate, EDM

is principally limited to the production of small series although some specific massproduction applications are known.

(d) Optimization of the electrical parameters - The choice of the electrical parameters of the

EDM-process depends largely on the material combination of electrode and work piece and

EDM manufactures only supply these parameters for a limited amount of material

combinations. When machining special alloys, the user has to develop his own technology.



Page 14

Chapter 2

Introduction-

In this chapter search few selected research paper related to EDM with effect of metal MRR,

TWR, OC, surface roughness (SR) workpiece material, we are broadly classified all the paper in

to five different category, i.e. paper related to material related workpiece or tool, tubular

electrode, tool design, some paper related to Effect of multiple discharge and rest of the paper

related to CNC.

2.1 Workpiece and tool material-

Dhar and Purohit [1] evaluates the effect of current (c), pulse-on time (p) and air gap voltage

(v) on MRR, TWR, ROC of EDM with Al–4Cu–6Si alloy–10 wt. % SiCP composites. This

experiment can be using the PS LEADER ZNC EDM machine and a cylindrical brass electrode

of 30 mm diameter. And three factors, three levels full factorial design was using and analyzing

the results. A second order, non-linear mathematical model has been developed for establishing

the relationship among machining parameters. The significant of the models were checked using

technique ANOVA and finding the MRR, TWR and ROC increase significant in a non-linear

fashion with increase in current.

Karthikeyan et .al [2] has presented the mathematical molding of EDM with aluminum-silicon

carbide particulate composites. Mathematical equation is Y =f(V , I , T ). And the effect of MRR,

TWR, SR with Process parameters taken in to consideration were the current (I), the pulse

duration (T) and the percent volume fraction of SiC (25 µ size). A three level full factorial

design was choosing. Finally the significant of the models were checked using the ANOVA.

The MRR was found to decrease with an increase in the percent volume of SiC, whereas the

TWR and the surface roughness increase with an increase in the volume of Sic. it shown the

graph between interactive effect of the percent volume of Sic and the current on MRR Fig 2.1.



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Figure 2.1 Graph between interactive effect of Sic and Current on MRR

Tool electrode material such as Al–Cu–Si–Tic composite produced using powder metallurgy

(P/M) technique and using workpiece material CK45 steel was shown by Taweel [3]. The central

composite second-order rotatable design had been utilized to plan the experiments, and RSM was

employed for developing experimental models. Composite electrode is found to be more

sensitive to peak current and Pulse on time then conventional electrode. And Fig 2.2. had shown

the multi response optimization result for maximum MRR and minimum TWR.

Figure 2.2 Multi Response optimization for Max. MRR and Min.TWR

B.Mohan and Satyanarayana [4] evolution the of effect of the EDM Current, electrode maritalpolarity, pulse duration and rotation of electrode on metal removal rate, TWR, and SR, and the

EDM of Al-Sic with 20-25 vol. % SiC, Polarity of the electrode and volume present of SiC, the

MRR increased with increased in discharge current and specific current it decreased with

increasing in pulse duration. Increasing the speed of the rotation electrode resulted in a positive

effect with MRR, TWR and better SR than stationary. The electric motor can be used to rotate

the electrode(tool) AV belt was used to transmit the power from the motor to the electrode



Page 16

Optimization parameters for EDM drilling were also developed to summarize the effect of

machining characteristic such as MRR, TWR and SR.

The effects of the machining parameters (MRR, TWR and SR) in EDM on the machining

characteristics of SKH 57 high-speed steel were investigated by Yan-Cherng et.al [5].

Experimental design was used to reduce the total number of experiments. Parts of the experiment

were conducted with the L18 orthogonal array based on the Taguchi method. Moreover, the

signal-to-noise ratios associated with the observed values in the experiments were determined by

ANOVA and F -test. The relationship of MRR and SR with pulse duration graph in different

peak current is as shown in Fig. 2.3. During the experiment MRR increases with peak current

MRR initially increased to a peak at around 100 µs, and then fell.

Figure 2.3 MRR and surface roughness with pulse duration graph

J. Simao et al [6] was developed the surface modification using by EDM, details are given of

operations involving powder metallurgy (PM) tool electrodes and the use of powders suspended

in the dielectric fluid, typically aluminum, nickel, titanium, etc. experimental results are

presented on the surface alloying of AISI H13 hot work tool steel during a die sink operation

using partially sintered WC / Co electrodes operating in a hydrocarbon oil dielectric. An L8

fractional factorial Taguchi experiment was used to identify the effect of key operating factors on

output measures (electrode wear, workpiece surface hardness, etc.). With respect to micro

hardness, the percentage contribution ratios (PCR) for peak current, electrode polarity and pulse

on time. Even so, the very low error PCR value (for micro hardness ~6%) implies that all the

major effects were taken into account.



Page 17

P. Narender Singh et al. [7] discuss the evolution of effect of the EDM current (C ), Pulse

ON-time (P) and flushing pressure (F ) on MRR, TWR, taper (T ), ROC, and surface roughness

(SR) on machining as-cast Al-MMC with 10% SiCp . And use of metal matrix composites.

ELEKTRAPULS spark erosion machine was used for the purpose and jet flushing of the

dielectric fluid, kerosene, was employed. Brass tool of diameter 2.7mm was chosen to drill the

specimens. An L27 OA, for the three machining parameters at three levels each, was opted to

conduct the experiments. ANOVA was performed and the optimal levels for maximizing the

responses were established. Scanning electron microscope (SEM) analysis was done to study the

surface characteristics.

A. Soveja et al [8] have defined the experimental study of the surface laser texturing of TA6Valloy. The influence of the operating factors on the laser texturing process has been studied using

two experimental approaches: Taguchi methodology and RSM. Empirical models have been

developed. They allowed us to determine a correlation between process operating factors and

performance indicators, such as surface roughness and MRR. Results analysis shows that the

laser pulse energy and frequency are the most important operating factors. Mathematical models,

that have been developed, can be used for the selection of operating factors’ proper values in

order to obtain the desired values of the objective functions.

Biing Hwa et al. [9] has discuss the investigates the feasibility and optimization of a

rotary EDM with ball burnishing for inspecting the machinability of Al2O3 /6061Al

composite using the Taguchi method. Three ZrO2 balls attached as additional components

behind the electrode tool offer immediate burnishing following EDM. Three observed values

machining rate, surface roughness and improvement of surface roughness are adopted to verify

the optimization of the machining technique. Design of tool electrode is Cupper ring shaped B-

EDM as shown in Fig 2.4. This B-EDM process approaches both a higher machining rate and a

finer surface roughness. Furthermore, the B-EDM process can achieve an approximately

constant machining rate.



Page 18

Figure 2.4 Design of Cu ring tool shaped B-EDM

Yan-Cherng Lin et al. [10] has reported that Electrical Discharge Energy on Machining of

Cemented Tungsten Carbide using an electrolytic copper electrode. The machining parameters

of EDM were varied to explore the effects of electrical discharge energy on the machining

characteristics, such as MRR , EWR, and surface roughness. Moreover, the effects of the

electrical discharge energy on heat-affected layers, surface cracks and machining debris were

also determined. The experimental results show that the MRR increased with the density of the

electrical discharge energy. The EWR and diameter of the machining debris were also related tothe density of the electrical discharge energy. When the amount of electrical discharge energy

was set to a high level, serious surface cracks on the machined surface of the cemented tungsten

carbides caused by EDM were evident

Lee and X.P.Li [11] showed the effect of the machining parameter in EDM of tungsten

carbide on the machining charatercteristics. The EDM process with tungsten carbide better

machining performances is obtaining generally with the electrode as the cathode and the

workpiece is anode. Tool with negative polarity give the higher material removal rate, lower tool

wear and better surface finish. High open circuit voltage is necessary for tungsten carbide due to

its high malting point and high hardness value and cupper tungsten as the tool electrode material

with tool electrode material with negative polarity. This study confirms that there exists an

optimum condition for precision machining of tungsten carbide although the condition may vary

with the composing of martial, the accuracy of the machine and other other external factor.



Page 19

Puertas and Luis[12] has define the optimization of machining parameter for EDM of Boron

carbide of conductive ceramic materials. It is these conditions that determine such important

characteristics as surface roughness, electrode wear, and MRR. In this article, a review of the

state of art of the die-sinking EDM processes for conductive ceramic materials, as well as a

description of the equipment used for carrying out the experiments, are presented. Also, a series

of mathematical models will be devised using design of experiments techniques combined with

multiple linear regression, which will allow us, while only performing a small number of

experiments, to select the optimal machining conditions for the finishing stage of the EDM

process.

Wang and Lin [13] discuss the optimization of W/Cu composite martial are used the Taguchimethod. W/Cu composites are a type of cooling material highly resistant to heat corrosion

produced through powder metallurgy. The Taguchi method and L18 orthogonal array to obtain

the polarity, peak current, pulse duration, duty factor, rotary electrode rotational speed, and gap-

load voltage in order to explore the material removal rate, electrode wear rate, and surface

roughness. The influenced of each variable and optimal processing parameter will be obtained

through ANOVA analysis through experimentation to improve the process.

Tsai et al [14] have working martial of graphite, copper and copper alloys are widely using

EDM because these materials have high melting temperature, and excellent electrical and

thermal conductivity. The electrodes made by using powder metallurgy technology from special

powders have been used to modify EDM surfaces in recent years, to improve wear and corrosion

resistance. Electrodes are made at low pressure (20 MPa) and temperature (200 °C) in a hot

mounting machine According to the experimental results, a mixing ratio of Cu–0wt%Cr and a

sinter pressure of 20 MPa obtained an excellent MRR. Moreover, this work also reveals that the

composite electrodes obtained a higher MRR than Cu metal electrodes. The recast layer was

thinner and fewer cracks were present on the machined surface.

Study of parameter in EDM by using the RSM, the parameter like MRR, TWR, gap size and

SR and relevant experimental data were obtained through experimentation by Sameh S.

Habib[15]. They are using Al/Sic composites material and shown the correlations between the

cutting rates, the surface finish and the physical material parameters of this process made it



Page 20

difficult to use. Optimal combination of these parameters was obtained for achieving controlled

EDM of the workpiece and finding the MRR increases with an increase of pulse on time, peak

current and gap voltage and MRR decreases with increasing of Sic%.

2.2 EDM with tubular electrode-

Saha and Choudhury [16] Study the process of dry EDM with tubular copper tool electrode

and mild steel workpiece. Experiments have been conducted using air and study the effect of gap

voltage discharge current, pulse-on time, duty factor, air pressure and spindle speed on MRR,

surface roughness (Ra) and TWR. Empirical models for MRR, Ra and TWR have then been

developed by performing a designed experiment based on the central composite design of

experiments. Response surface analysis has been done using the developed models. ANOVA

tests were performed to identify the significant parameters. The dry EDM attachment has shown

the experimental result in Fig 2.5, and finding the Flow characteristic of air in the inter-electrode

gap affects the MRR and the surface roughness (Ra). There exists an optimum number of air-

flow holes (in the tool) for which the MRR is highest and the Ra is lowest.

Figure 2.5 Experimental set-up

In the process of milling EDM machining of complex cavities with simple cylindrical or

tubular electrodes was shown by Bleys et al. [17]. Milling EDM requires compensation of the

tool electrode wear. Existing wear compensation methods are mostly based on off-line prediction

of tool wear. New wear compensation method, incorporating real-time wear sensing based on

discharge pulse evaluation. Tool wear is continuously evaluated during machining, and the actual

wear compensation is adapted on the basis of this real-time wear evaluation. As a solution to

this problem, a new wear compensation method is developed, based on real-time tool

wear sensing. Simulations and experiments show the potential of the new method.



Page 21

In this method for pipe electrode for a small hole for EDM or electrode magazine for

replacing quickly a pipe electrode small-hole electric discharge machining to make a small-hole

in a work by electric discharge machining was developed by Suzuki [18] they have to make

replacement of a pipe electrode, an electrode magazine containing an electrode guide in which

the pipe electrode is accommodated is replaced by using means. The electrode magazine has a

self-position maintenance tip for maintaining the position taken by the electrode until then while

the electrode magazine is removed from the electrode discharge machine and resuming the

electrode discharge from the position after the electrode magazine is attached again to the

electric discharge machine.

Lin and Han [19] presented the study about tube electrode for an EDM drilling includes a

stabilizer block and a mover. The stabilizer block has a concaved in shaped supporting wall that

parallels to the traveling path of a tube electrode, and has a plurality of apertures interconnected

to air vacuuming connections to suck air. The move is connected to the stabilizer block for

approaching the tube electrode. Suction force pushes the tube electrode against the supporting

wall to achieve stabilization of the tube electrode. The stabilizer block further has a sensor to

detect whether the tube electrode is seated into the stabilizer block or not and to measure the

available length of the tube electrode before or after drilling.

2.3 EDM tool design –

Sohani et al. [20] discussed about sink EDM process effect of tool shape and size factor

are to be considering in process by using RSM process parameters like discharge current, pulse

on-time, pulse off-time, and tool area. The RSM-based mathematical models of MRR and TWR

have been developed using the data obtained through central composite design. The analysis of

variance was applied to verify the lack of fit and adequacy of the developed models. The

investigations revealed that the best tool shape for higher MRR and lower TWR is circular,

followed by triangular, rectangular, and square cross sections. From the parametric analysis, it is

also observed that the interaction effect of discharge current and pulse on-time is highly

significant on MRR and TWR, whereas the main factors such as pulse off-time and tool area are

statistically significant on MRR and TWR.



Page 22

Zhon and Han [21] worked on servo system for EDM, adaptive control of with self turning

regulator a new EDM adaptive control system which directly and automatically regulates tool-

down-time has been developed. Based on the real-time-estimated parameters of the EDM

process model, by using minimum-variance control strategy, the process controller, a self-tuning

regulator, was designed to control the machining process so that the gap states follow the

specified gap state. With a properly selected specified gap states, this adaptive system improves

the machining rate by, approximately, 100% and in the meantime achieves a more robust and

stable machining than the normal machining without adaptive control. This adaptive control

system helps to gain the expected goal of an optimal machining performance.

2.4 Effect of multiple discharges of EDM-

The EDM process e workpiece generated by the superposition of multiple discharges, as it

happens during an actual EDM operation, by Izquierdo et al. [22] diameter of the discharge

channel and material removal efficiency can be estimated using inverse identification from the

results of the numerical model.

An original numerical model for simulation of the EDM processhas been presented. The model generates EDM surfaces by calculating temperature fields inside

the workpiece using a finite difference-based approach, and taking into account the effect of

successive discharges.

Wei Bin et al. [23] has study about electrical discharge machining with multiple holes in an

electrically conductive work piece, includes an electrical discharge machine for rotatable

mounting a first electrode, and at least one electrical discharge unit for rotatable mounting at

least one second electrode. The electrical discharge machine includes a driver and a controller,

the driver is desirably coupled to the electrical discharge machine and the electrical discharge

unit for rotating the first electrode and the at least one second electrode, and the controller is

desirably coupled to the electrical discharge machine and the at least one electrical discharge unit

for controlling a supply of electrical energy from the first electrode and second electrode to the

workpiece.



Page 23

Kunge et al. [24] evolution the effect of MRR and EWR study on the powder mixed

electrical discharge machining (PMEDM) of cobalt-bonded tungsten carbide (WC-Co) has been

carried out. In the PMEDM process, the aluminum powder particle suspended in the dielectric

fluid disperses and makes the discharging energy dispersion uniform; it displays multiple

discharging effects within a single input pulse. This study was made only for the finishing stages

and has been carried out taking into account the four processing parameters: discharge current,

pulse on time, grain size, and concentration of aluminum powder particle for the machinability

evaluation of MRR and EWR. The RSM has been used to plan and analyze the experiments.

Notice that the residuals generally fall on a straight line implying that the errors are normally

distributed. Furthermore, this supports adequacy of the least squares fit. The MRR generally

increases with an increase of Aluminum powder concentration.

2.5 CNC Electric discharge machining-

Ding and Jiang [25] presented the work on CNC EDM machining of free-form surfaces

requires tool paths that are different from those used in mechanical milling although in geometry

both processes are described by the similar model of intersection between the rotating tool and

the Workpiece. Special requirements on tool paths demanded by CNC EDM machining arestudied and a two-phase tool path generation method for 4-axis CNC EDM rough milling with a

cylindrical electrode is developed. The solid model of the workpiece and interface between the

electrode as shown in Fig 2.6 And finding the Discharge gap compensation, electrode wear

compensation and many other factors have to be considered in the tool path generation process.

Figure 2.6 Solid model of workpiece and interference between work and tool



Page 24

Bleys et al. [26] has discuss about CNC contouring EDM with a rotating cylinder and or

tubular electrode necessitates compensation of the tool electrode wear in CNC milling operation

is based on off-line tool wear simulation prior to machining. Tool wear can therefore be

compensated in one dimension, by continuously moving the tool downward, On-line estimation

of tool wear is used for combining anticipated compensation with real-time compensation. This

extends the scope of milling EDM to the machining of blanks of which the exact shape is not

known in advance.

Study about Variable structure system (VSS) with the large proportional gains can suddenly

hold the electrode at the appropriate position was shown by Fang chang [27] for design process

of the VSS is presented according to a practical gap control system for an EDM. This advantage

can provide high performance on the nonlinear and time-varying gap condition during eroding

process. The practical experimental results of an EDM with the VSS controller show a decrease

of machining time, compared to the time required by the conventional proportional controlled

EDM. And experimental result obtain from the commercial CNC EDM indicate that the eroding

speed of control EDM with VSS faster than speed with force P control system.

Chang and Chiu [28] presented the electrode wear compensation of EDM of the scanning

process with using the robust gap control is applied to compensate for electrode wear in an

electric discharge scanning (ED-Scanning) process. This control compensates for the wear

without reference to the wear ratio of the electrodes. As the tool moves horizontally from part (a)

to part (b) as shown in Fig 2.7, compensation for wear they are discharge occur in gap and the

material is then removed .The electrode must be moved from Z2 to Z1 and maintain the depth of

removal at a layer. Finally During scanning the robust controller can compensate for wear on the

bottom of the electrode without a complex calculation.



Page 25

Figure 2.7 Compensation for wear during scanning of a layer

Ziada and Koshy [29] Study about the process Rotating Curvilinear Tools for EDM of

Polygonal Shapes with Sharp Corners, Flushing of the inter-electrode gap is of critical

importance in the performance of electrical discharge sinking operations. When the provision of

flushing holes in the tool or the Workpiece is impractical, effective flushing is best realized by

inducing a relative motion between the electrodes. This innovative scheme enables the

machining of regular as well as non-regular polygonal shapes with sharp corners.

Experimental results from implementing this concept on a 4-axis CNC EDM machine tool are

presented.

Study on reducing contour errors for CNC EDM was shown by Shieh and lee [30] they are

proposed control, scheme consists of three portions. First, the step control performs position

loop controller for each individual axis. Second, control error calculations suitable for control

system analysis and design are used, and third, cross-coupling control is used to control contour

error. Under the control of the proposed scheme, the stability of the system is studied for both

linear and circular trajectories. The experimental results of a CNC EDM show that the

proposed scheme is effective to improve contouring performance and ready for practical

implementation.



Page 26

2.6 Objective of the present work-

From the research papers in this classification, it is observed that few works has been

reported on EDM on the material Al-Sic, EN-19, SKH 57, AISI H13, AISI D2 tool steel, and

various composite materials. Study on EDM of different material and different mathematical

model can be use to validated the experimental results.

The objective of the present work is an attempt to finding feasibility of machining AISI P-20

tool steel using U-shaped tubular copper electrode and internal flushing. The machining

parameter selected for discharge current, pulse on time, and diameter of the tool using Taguchi

design approach analyzing the responses MRR, TWR, and over cut.



Page 27

Chapter 3

Introduction

In this chapter we are going to discuss about the experimental work which is consist

about formation of the L-18 orthogonal array based on Taguchi design, orthogonal array is

reduces the total on of experiment, in this experiment total 18 run. And Experimental set up,

selection of workpiece, tool design, and taking all the value and calculation of MRR, TWR, and

OC.

3.1 Experimental set up

For this experiment the whole work can be down by Electric Discharge Machine, model

ELECTRONICA- ELECTRAPULS PS 50ZNC (die-sinking type) with servo-head (constant

gap) and positive polarity for electrode was used to conduct the experiments. Commercial grade

EDM oil (specific gravity= 0.763, freezing point= 94˚C) was used as dielectric fluid. With

internal flushing of U-shaped cu tool with a pressure of 0.2 kgf/cm2 .Experiments were

conducted with positive polarity of electrode. The pulsed discharge current was applied in

various steps in positive mode.

The EDM consists of following major part as shown in the chapter Appendix (Fig 5.1)

3.1.1 Dielectric reservoir, pump and circulation system.

3.1.2 Power generator and control unit.

3.1.3 Working tank with work holding device.

3.1.4 X-y table accommodating the working table.

3.1.5 The tool holder.

3.1.6 The servo system to feed the tool.



Page 28

3.1.1 Dielectric reservoirs pump and circulation system - Dielectric reservoirs and

pump are used to circulate the EDM oil for every run of the experiment and also used the filter

the EDM oil. Dielectric reservoir is shown in Fig 3.1.

Figure 3.1 Dielectric reservoir

3.1.2 Power generator and control unit - The power supply control the amount of energy

consumed. First, it has a time control function which controls the length of time that current

flows during each pulse; this is called “on time.” Then it is control the amount of current

allowed to flow during each pulse. These pulses are of very short duration and are measured in

microseconds. There is a handy rule of thumb to determine the amount of current a particular

size of electrode should use: for an efficient removal rate, each square inch of electrode calls

for 50 A. Low current level for large electrode will extend overall machine time unnecessarily.

Conversely, too heavy a current load can damage the workpiece of electrode.

The control unit is control the all function of the machining for example of Ton, Ip, duty

cycle, putting the values and maintain the workpiece the tool gap. The control unit is shown in

this Fig 3.2.



Page 29

Figure 3.2 Control unit of EDM machine

3.1.3 Working tank with work holding device– All the EDM oil kept in the working tank

working tank is used to the supply the fluid during the process of machining.

3.1.4 X-y table accommodating the working table – They are used to the moment of the

workpiece form X and Y direction.

3.1.5 The tool holder –The tool holder hold the tool with the process of machining. The tool

holder with workpiece and tool as shown in Fig 3.3

.

Figure 3.3 Tool holder with Workpiece and tool



Page 30

3.1.6 The servo system to feed the tool - The servo control unit is provided to maintain the

pre determined gap. It senses the gap voltage and compares it with the present value and thedifferent in voltage is then used to control the movement of servo motor to adjust the gap.

3.2 Selection of the work piece-

It is capable of machining of hard material component such as heat treated tool steels,

composites, super alloys, ceramics, carbides, heat resistant steels etc. The higher carbon grades

are typically used for such applications as stamping dies, metal cutting tools, etc. AISI grades of

tool steel is the most common scale used to identify various grades of tool steel. Individual alloys

within a grade are given a number; for example: A2, O1, D2, P20 etc.

In this experiment using AISI P20 tool steel material this P-20 tool steel material is a pre

hardened high tensile tool steel which offers ready machine ability in the hardened and tempered

condition, therefore does not require further heat treatment. Subsequent component

modifications can easily be carried out.

Plastic mould steel (P-20 tool steel) that is usually supplied in a hardened and tempered

condition. Good machine ability, better polish ability, compared to DIN 1.2312 (AISI P20+S).

Plastic mould steel is used growing range of to Plastic moulds, frames for plastic pressure dies,

hydro forming tools. And their composition of the tool is listed in this Table: 3.1, 3.2, 3.3 and

3.4.

Table 3.1 Composition of AISI P-20 tool steel material

Elements Weight limit % Actual weight %C 0.28-0.40 0.40

Mn 0.60-1.00 1.00

Si 0.20-0.80 0.40

Cr 1.40-2.00 1.20

Mo 0.30-0.55 0.35

Cu 0.25 0.25

P 0.03 0.03

S 0.03 0.03



Page 31

Table 3.2 AISI P20 tool steel categories

Category Steel

Class Tool steel

Type General mold steel

Designations Germany : DIN 1.2330

United States : ASTM A681 , UNS T51620

Table 3.3 Mechanical properties of P20 steel

Properties ConditionsT (°C)

Density 7.85x1000 kg/m3 25

Poisson’s Ratio 0.27-0.30 25

Elastic Modulus 190-210Gpa 25

Table 3.4 Thermal Properties of P20 tool steel material

Properties

ConditionsT (°C)

Thermal Expansion (10-6 /ºC) 12.8 20-425 more

AISI P20 tool steel material and after machining workpiece and the Cu U-shaped tool. As

showing Fig 3.4 and the workpiece shows 18 total no. of experiments doing in this job.



Page 32

Figure 3.4 P-20 workpiece before and after machining with tool

3.3 Tool Design- The tool design for Electric discharge machining for using Cu, brass, Al

alloys silver tungsten alloys etc. In this experiment using the copper tool electrode and the design

of cupper tool is a U- shaped with internal flashing. Shapes of the tool same cavity produced in

the workpiece. Using the U-shaped tool so U-shaped cavity produced on the workpiece. The

design of the tool in showed in Fig 3.5 and 3.6.



Page 33

Figure 3.5 U - Tube Copper tool design

Figure 3.6 U-shaped Copper tool



Page 34

3.4 Flow chart of experiment

Workpiece = AISI P20 Tool steelTool = Cu Tube U-shaped

Machining parameter

Diameter of the tool (D)

Pulse duration (Ton)

Discharge current (Ip)

Experiment Techniques

Inputs

Experimentations

Analysis the result

Taguchi method

MRR TWR OC

Output/

Responses

Experimental flow chat



Page 35

3.5 Mechanism of MRR

The mechanism of material removal of EDM process is most widely established principle

is the conversion of electrical energy it into thermal energy. During the process of machining the

sparks are produced between workpiece and tool .Thus each spark produces a tiny crater, and

crater formation shown in this Fig 3.7 in the material along the cutting path by melting and

vaporization, thus eroding the workpiece to the shape of the tool.

Figure 3.7 Crater formation in EDM process

It is well-known and elucidated by many EDM researchers by Roethel et.al [31] that

Material Removal Mechanism (MRM) is the process of transformation of material elements

between the work-piece and electrode. The transformation are transported in solid, liquid or

gaseous state, and then alloyed with the contacting surface by undergoing a solid, liquid or

gaseous phase reaction.

3.5.1 Evaluation of MRR-

The material MRR is expressed as the ratio of the difference of weight of the workpiece

before and after machining to the machining time and density of the material.

MRR=

………………………… (3.1)

Whereas Wjb = Weight of workpiece before machining.

Wja = Weight of workpiece after machining.



Page 36

t = Machining time = 1.00 hr.

ρ = Density of AISI P20 steel material =7.84gm/cm3

3.6 Mechanism of Tool wears-

Tool wear is an important factor because if affects dimensional accuracy and the shape

produced. Tool wear is related to the melting point of the materials. Tool wear is affected by the

precipitation of carbon from the hydrocarbon dielectric on the electrode surface during sparking.

By Mohri et al. [32] Also the rapid wear on the electrode edge was because of the failure of

carbon to precipitate at difficult to reach regions of the electrode.

3.6.1 Evaluation of tool wear rate

TWR is expressed as the ratio of the difference of weight of the tool before and after

machining to the machining time. That can be explain this equations

TWR =

…………………(3.2)

Whereas Wtb = Weight of the tool before machining.

Wta = Weight of the tool after machining.

t = Machining time (In this experiment the machining time is one hour).

3.7 Mechanism of over cut -

It is the discharge by which the machined hole in the work piece exceeds the electrode

size and is determined by both the initiating voltage and the discharge energy. During the process

of machining EDMed cavity produced are always larger than the electrode this def erence (size of

electrode and cavity) is called Over Cut (OC). It becomes important when close tolerance



Page 37

components are required to be produced for space application and also in tools, dies and moulds

for press work (Singh and Maheshwari [33]).

3.7.1 Evaluation of over cut

OC is expressed as half the difference of diameter of the hole produced to the tool

diameter that is shown in these equations.

OC =

…………………….(3.3)

Whereas Djt = diameter of hole produced in the workpiece

Dt = Diameter of tool

3.8 Taguchi design

Dr. Genichi Taguchi is regarded as the foremost proponent of robust parameter design,

which is an engineering method for product or process design that focuses on minimizing

variation and/or sensitivity to noise. When used properly, Taguchi designs provide a powerful

and efficient method for designing products that operate consistently and optimally over a

variety of conditions. Taguchi proposed several approaches to experimental designs that are

sometimes called "Taguchi Methods." These methods utilize two-, three-, four-, five-, and

mixed-level fractional factorial designs. Taguchi refers to experimental design as "off-line

quality control" because it is a method of ensuring good performance in the design stage of

products or processes.

3.9 Taguchi design experiments in MINITAB

MINITAB provides both static and dynamic response experiments in a static response

experiment; the quality characteristic of interest has a fixed level. The goal of robust

experimentation is to find an optimal combination of control factor settings that achieve

robustness against (insensitivity to) noise factors. MINITAB calculates response tables and

generates main effects and interaction plots for:-



Page 38

Signal-to-noise ratios (S/N ratios) vs. the control factors.

Means (static design) vs. the control factors.

A Taguchi design or an orthogonal array the method is designing the experimental

procedure using different types of design like, two, three, four, five, and mixed level. In the

study, a three factor mixed level setup is chosen with a total of eighteen numbers of experiments

to be conducted and hence the OA L18 was chosen. This design would enable the two factor

interactions to be evaluated. As a few more factors are to be added for further study with the

same type of material, it was decided to utilize the L18 setup, which in turn would reduce the

number of experiments at the later stage. In addition, the comparison of the results would be

simpler.The levels of experiment parameters electrode diameter (D), spark on time (Ton), and

discharge current (Ip) are shown in Table 3.5 and the design matrix is depicted in Table 3.6.

Table 3.5 Machining parameters and their level

Machining parameter Symbol Unit Level

Level 1 Level 2 Level 3

Electrode diameter (D) mm 4 6Spark on time (Ton) µs 50 500 1000

Discharge current (Ip) A 1 3 5

3.10 Conduct of Experiment –

P20 Tool steel material particulate was using U-shaped Copper tube tool with 4mm and

6mm diameter. And the PS 50ZNC (die-sinking type) of EDM machine are used. Commercial

grade EDM oil (specific gravity= 0.763, freezing point= 94˚C) was used as dielectric fluid.

Internal flushing with U-shaped copper tool with internal flushing was used to flush away the

eroded materials from the sparking zone. In this experiment voltage and duty cycle is kept

constant is 50 v and 8. For a three factor are tackled with a total number of 18 experiments

performed on die sinking EDM.

The calculation of material removal rate and tool wear rate by using electronic balance

weight machine as shown in Fig 5.2. This machine capacity is 300 gram and accuracy is 0.001



Page 39

gram. And the over cut measurement can be using tool maker microscope as shown in Fig 5.3

this machine accuracy is 0.0001 mm .

3.11 Design matrix and Observation table

Table 3.6 Design matrix and Observation table

Run

Dia(mm)

Ip (A) Ton (µs)

Wt of Workpiece (gm)

Wt. of Tool

(gm)

Cavity dia.

(mm)

Wjb Wja Wtb Wta Djt

1 4 1 50 266.510 266.220 18.976 18.974 5.724

2 4 1 500 266.220 266.109 18.974 18.970 5.393

3 4 1 1000 266.109 266.093 18.970 18.969 4.736

4 4 3 50 266.093 264.914 18.969 18.941 5.882

5 4 3 500 264.914 264.483 18.941 18.926 5.743

6 4 3 1000 264.488 264.395 18.926 18.925 5.445

7 4 5 50 264.395 262.983 18.925 18.836 5.895

8 4 5 500 262.983 262.146 18.836 18.827 5.785

9 4 5 1000 262.146 262.061 18.827 18.801 5.964

10 6 1 50 81.783 81.491 22.214 22.196 6.143

11 6 1 500 81.922 81.783 22.224 22.214 6.089

12 6 1 1000 81.955 81.922 22.225 22.224 6.071

13 6 3 50 3841.0 3840.0 22.240 22.238 6.158

14 6 3 500 82.769 82.245 22.238 22.233 6.130

15 6 3 1000 82.245 81.955 22.233 22.225 6.144

16 6 5 50 269.264 267.862 22.196 22.187 6.180

17 6 5 500 267.862 266.807 22.187 22.161 6.136

18 6 5 1000 266.807 266.510 22.161 22.173 6.024



Page 40

3.12 Conclusion-

Experiments were conducted according to Taguchi method by using the machining set up

and the designed U-shaped tubular electrodes with internal flushing. The control parameters like

diameter of electrode (D) , discharge current (Ip) and pulse duration (Ton) conductivity were

varied to conduct 18 different experiments and the weights of the work piece and Tool and

dimensional measurements of the cavity were taken for calculation of MRR , TWR and over

cuts.



Page 41

Chapter 4

Introduction –

In This chapter are related about influences of MRR, TWR, and OC and finding the result

which factors discharge current , pulse duration, diameter of Cu tool , is most important with

help of Taguchi method.

4.1 Response table –The response table for MRR, TWR and OC are shown in Table 4.1 along with the input

factors.

Table 4.1 Response table

Run Dia

(mm)

Ip

(A)

Ton

(µs)

MRR

(mm3 /min)

TWR

(gm/min)

OC

(mm)

1 4 1 50 1.0400 0.0170 0.8620

2 4 1 500 0.2360 0.0030 0.6965

3 4 1 1000 0.0360 0.0006 0.3680

4 4 3 50 3.9890 0.0660 0.9410

5 4 3 500 0.9040 0.0150 0.8715

6 4 3 1000 0.7970 0.0130 0.7225

7 4 5 50 2.9980 0.0400 0.9295

8 4 5 500 1.7770 0.0290 0.8790

9 4 5 1000 0.8000 0.0030 0.9820

10 6 1 50 0.6140 0.0103 0.1435

11 6 1 500 0.2950 0.0040 0.0895

12 6 1 1000 0.0700 0.0010 0.071013 6 3 50 3.0000 0.0500 0.5790

14 6 3 500 1.1120 0.0180 0.5650

15 6 3 1000 0.9738 0.0356 0.5720

16 6 5 50 2.9700 0.0490 0.5900

17 6 5 500 2.2390 0.0370 0.5680

18 6 5 1000 1.3000 0.0105 0.5120



Page 42

4.2 Influences on MRR

The S/N ratios for MRR are calculated as given in Equation 4.1. Taguchi method is used to

analysis the result of response of machining parameter for larger is better criteria.

LB: η 10 log

∑ yi

] . . . . . . . . . . (4.1)

Where η denotes the S/N ratios calculated from observed values, yi represents the

experimentally observed value of the ith experiment and n=1 is the repeated number of each

experiment in L-18 OA is conducted.

The analysis of variances for the factors is shown in Table 4.2 which is clearly indicates

that the diameter of the tool is not important for influencing MRR and Ip and Ton are the most

influencing factors for MRR and as well as the interaction Ip x Ton is significant (shown in

bold). And other factors are not significant .The delta values are Dia. of tool, Ton and Ip are

1.1493, 15.0841 and 18.3901 respectively, depicted in Table 4.3. The case of MRR, it is “Larger

is better”, so from this table it is clearly definite that Ip is the most important factor then Ton and

last is dia. of the tool.

Table 4.2 Analysis of Variance for S/N ratios for MRR

Source DF Seq SS Adj SS Adj MS F P

Dia 1 5.94 5.94 5.944 3.38 0.140

Ip 2 1222.40 1222.40 611.198 347.29 0.000

Ton 2 683.05 683.05 341.524 194.06 0.000

Dia*Ip 2 2.17 2.17 1.087 0.62 0.584

Dia*Ton 2 30.98 30.98 15.491 8.80 0.034

Ip*Ton 4 163.28 163.28 40.820 23.19 0.005

Residual Error 4 7.04 7.04 1.760

Total 17 2114.86



Page 43

Table 4.3 Response for S/N Rations Larger is better (MRR)

Level Diameter Ip Ton

1 -2.1459 -13.1689 6.1093

2 -0.9966 3.2340 -1.8508

3 5.2212 -8.9721

Delta 1.1493 18.3901 15.0841

Rank 3 1 2

During the process of Electrical discharge machining, the influence of various machining

parameter like Ip, Ton and Diameter of tool has significant effect on MRR, as shown in main

effect plot for S/N ratio of MRR in Fig 4.1. The discharge current (Ip) is directly proportional to

MRR in the range of 1 to 3A. This is expected because an increase in pulse current produces

strong spark, which produces the higher temperature, causing more material to melt and erode

from the work piece. Besides, it is clearly evident that the other factor does not influence much

as compared to Ip and similar conclusions were shown by Ghoreishi and Tabari [34]. But, with

increase in discharge current from 3A to 5A MRR increases slightly. However, MRR decreases

monotonically with the increase in pulse on time.

The diameter of the tool has no significant effect on MRR. The interaction plot of MRR

is shown in Fig 4.2, where each plot exhibits the interaction between three different machining

parameters like Ip, Ton and dia. of tool. This implies that the effect of one factor is dependent

upon another factor. It is also confirmed by the ANOVA table (Table 4.2).

It is well known fact that the spark energy increases with Ton and hence, MRR increases

with Ton in the range of 300 to 400 µs. MRR usually increases with Ton up to a maximum value

after which that it starts to decrease. This is due to the fact that with higher Ton, the plasma

formed between the Inter electrode gap (IEG) actually hinders the energy transfer and thus

reduces MRR. In this experiment the value of pulse durations are 50, 500 and 1000 µs which

miss the peak values. So, the plotted graph of pulse duration vrs MRR, as show decreasing trend

only.



Page 44

Figure 4.1 Main effect plot for S/N ratios (MRR)

Figure 4.2 Interaction plot for MRR



Page 45

4.2.1 Model Analysis of MRR

The coefficients of model for S/N ratios for MRR are shown in Table 4.4. The parameter

R2 describes the amount of variation observed in MRR is explained by the input factors. R2 =

99.7 % indicate that the model is able to predict the response with high accuracy. Adjusted R2 is

a modified R2 that has been adjusted for the number of terms in the model. If unnecessary terms

are included in the model, R2 can be artificially high, but adjusted R2 (=98.6 %.) may get smaller.

The standard deviation of errors in the modeling, S= 1.327. Comparing the p-value to a

commonly used α-level = 0.05, it is found that if the p-value is less than or equal to α, it can be

concluded that the effect is significant (shown in bold), otherwise it is not significant.

Table 4.4 Estimated Model Coefficients for SN ratios

Term Coef SE Coef T P

Constant -1.5712 0.3127 -5.025 0.007

Dia 4 -0.5747 0.3127 -1.838 0.140

Ip 1 -11.5976 0.4422 -26.227 0.000

Ip 3 4.8052 0.4422 10.866 0.000

Ton 50 7.6805 0.4422 17.369 0.000

Ton 500 -0.2796 0.4422 -0.632 0.562

Dia*Ip 4 1 0.0519 0.4422 0.117 0.912

Dia*Ip 4 3 0.3973 0.4422 0.898 0.420Dia*Ton 4 50 1.7636 0.4422 3.988 0.016

Dia*Ton 4 500 -0.3827 0.4422 -0.865 0.436

Ip*Ton 1 50 3.5404 0.6254 5.661 0.005

Ip*Ton 1 500 1.8758 0.6254 3.000 0.040

Ip*Ton 3 50 -0.1346 0.6254 -0.215 0.840

Ip*Ton 3 500 -2.9316 0.6254 -4.688 0.009

S=1.327 R-Sq=99.7% R-Sq(adj)=98.6%

The residual plot of MRR is shown in Fig 4.3. This layout is useful to determine whether

the model meets the assumptions of the analysis. The residual plots in the graph and the

interpretation of each residual plot indicate below:

a. Normal probability plot indicates the data are normally distributed and the variables

are influencing the response. Outliers don’t exist in the data, because standardized

residues are between -2 and 2.

b. Residuals versus fitted values indicate the variance is constant and a nonlinear

relationship exists as well as no outliers exist in the data.



Page 46

c. Histogram proves the data are not skewed and not outliers exist.

d. Residuals versus order of the data indicate that there are systematic effects in the

data due to time or data collection order.

Standardized Residual

P e r c e n t

210-1-2

99

90

50

10

1

Fitted Value

S t

a n d a r d i z e d R e s i d u a l

100-10-20-30

2

1

0

-1

-2


F r e q u e n c y

210-1-2

4

3

2

1

0

Observation Order

S t a n d a r d i z e d R e s i d u a l

18161412108642

2

1

0

-1

-2

Normal Probability Plot of the Residuals Residuals Versus the Fitted Values

Histogram of the Residuals Residuals Versus the Order of the Data

Residual Plots for SN ratios (MRR)

Figure 4.3 Residual plot for MRR

4.3 Influences on TWR

The S/N ratios for TWR are calculated as given in Equation 4.2. Taguchi method is used

to analysis the result of response of machining parameter for smaller is better (SB) criteria.

SB: 10log

∑ . . . . . . . . . . . (4.2)

The analysis of variances for the factors are Dia, Ip , Ton, and IpxTon as shown in Table 4.5

is clearly indicate that the diameter of the tool is not important for influencing TWR and the

value of Ip and Ton is most effected the TWR and as well as interaction Ip x Ton significant are

shown in bold and otherwise not significant. The delta values are Dia. of tool, Ip and Ton are



Page 47

2.81, 18.36 and 17.04 respectively, in Table 4.6. The case of TWR Smaller is better, so from this

table it is clearly definite that Ip is the most important factor then Ton and last is dia.of the tool.

Table 4.5 Analysis of Variance for TWR


Dia 1 35.46 35.46 35.465 17.02 0.015

Ip 2 1185.01 1185.01 592.506 284.31 0.000

Ton 2 871.24 871.24 435.618 209.03 0.000

Dia*Ip 2 12.42 12.42 6.209 2.98 0.161

Dia*Ton 2 71.66 71.66 35.828 17.19 0.011

Ip*Ton 4 243.68 243.68 60.921 29.23 0.003

Residual Error 4 8.34 8.34 2.084

Total 17 2427.81

Table 4.6 Response Table for Signal to Noise Ratios Smaller is better (TWR)

During the process of EDM, the influence of various machining parameter like Ip, Ton

and Diameter of tool has significant effect on TWR , as shown in main effect plot for S/N ratio

of TWR in Fig 4.4. Increasing in the discharge current from 1 to 3 A the tool wear rate is

decreasing, but discharge Current in the range of 3 to 5 A the tool wear rate is increasing.

Because of Ip increases the pulse energy increases and thus more heat energy is produced in the

tool work piece interface, leads to increase the melting and evaporation of the electrode. One can

interpret that Ip has a significant direct impact on TWR By Dhar and Purohit [1]. And pulse on

time is directly proportional to the tool wear rate. And diameter of the tool has no significant

effect on TWR. The interaction plot of TWR is shown in Fig 4.5, where each plot exhibits the

interaction between three different machining parameters like Ip Ton and dia. of tool. This

implies that the effect of one factor is dependent upon another factor. It is also confirmed by the

ANOVA table (Table 4.5).


1 39.70 49.66 29.82

2 36.89 31.28 38.20

3 33.93 46.86

Delta 2.81 18.36 17.04

Rank 3 1 2



Page 48

Figure 4.4 Main effect plot for SN ratios (TWR)

Figure 4.5 Interaction plot for TWR



Page 49

4.3.1 Model Analysis of TWR

The coefficients of model for S/N ratios for TWR are shown in Table 4.7. The parameter

R2 (amount of variation)= 99.7% , Adj R2 = 98.5% , and standard deviation of error in themolding S= 1.444. And comparing the p value (less than 0.05) it can be concluded that the effect

is significant (shown in bold), otherwise it is not significant.

Table 4.7 Estimated Model Coefficients for SN ratios (TWR)


Constant 38.2922 0.3403 112.537 0.000

Dia 4 1.4037 0.3403 4.125 0.015

Ip1 11.3724 0.4812 23.633 0.000

Ip3 -7.0097 0.4812 -14.567 0.000Ton 50 -8.4723 0.4812 -17.607 0.000

Ton 500 -0.0960 0.4812 -0.199 0.852

Dia*Ip 4 1 -0.9731 0.4812 -2.022 0.113

Dia*Ip 4 3 -0.0833 0.4812 -0.173 0.871

Dia*Ton 4 50 -2.2372 0.4812 -4.649 0.010

Dia*Ton 4 500 -0.3706 0.4812 -0.770 0.484

Ip*Ton 1 50 -3.6251 0.6805 -5.327 0.006

Ip*Ton 1 500 -0.3604 0.6805 -0.530 0.624

Ip*Ton 3 50 2.0048 0.6805 2.946 0.042Ip*Ton 3 500 4.4999 0.6805 6.612 0.003

S = 1.444 R-Sq = 99.7% R-Sq(adj) = 98.5%

The residual plot of TWR is shown in Fig 4.6. This residual plot in the graph and the

interpretation of each residual plot indicate below.

a) Normal probability plot indicate outlines don’t exist in the data, because standardized

residues are between -2 and 2.

b) Residuals versus fitted values indicate the variation is constant.

c) Histogram shows the data are not skewed and not outline exist.

d) Residual versus order of the data indicate that systematic effects in the data due to time of

data collection order.



Page 50


P e r c e n t

210-1-2

99

90

50

10

1

Fitted Value

S t a n d a r d i z e d R e s

i d u a l

6050403020

2

1

0

-1

-2


F r e q u

e n c y

210-1-2

4

3

2

1

0

Observation Order

S t a n d a r d i z e

d R e s i d u a l

18161412108642

2

1

0

-1

-2



Residual Plots for TWR

Figure 4.6 Residual Plots for TWR

4.4

Influences on over cut –

The S/N ratios for OC are calculated as given in Equation 4.2. Taguchi method is used to

analysis the result of response of machining parameter for smaller is better (SB) criteria.

The analysis of variances for the factors are Dia, Ip , Ton, and IpxTon as shown in Table

4.8 is clearly indicate that the interaction factors Ton x Dia. and Ton x Ip is not significant for

OC and the value of Ip is most influencing of OC and also Dia. of tool is significant (shown in

bold). The delta values are Dia. of tool, Ip and Ton are 7.900, 9.449 and 2.777 respectively, in

Table 4.6. The case of OC Smaller is better, so from this table it is clearly definite that Ip is the

most important factor then dia.of the tool and last is Ton.



Page 51

Table 4.8 Analysis of Variance for SN ratios (OC)


Dia 1 280.812 280.812 280.812 242.40 0.000

Ip 2 345.662 345.662 172.831 149.19 0.000

Ton 2 23.182 23.182 11.591 10.01 0.028

Dia*Ip 2 144.814 144.814 72.407 62.50 0.001

Dia*Ton 2 0.965 0.965 0.482 0.42 0.685

Ip*Ton 4 24.310 24.310 6.077 5.25 0.069

Residual Error 4 4.634 4.634 1.158

Total 17 824.379

Table 4.9 Response for S/N Rations smaller is better (Over cut)


1 2.175 12.319 4.774

2 10.074 3.184 6.049

3 2.871 7.551

Delta 7.900 9.449 2.777

Rank 2 1 3

The over cut between the dimension of the electrode and the size of the cavity it is

inherent to the EDM process which is unavoidable though adequate compensation are provided

at the tool design. To achieve the accuracy, minimization of over cut is essential. Therefore

factors affecting of over cut is essential to recognize. The over cut are effect to each parameter

such as diameter of tool, discharge current and pulse on time, the main effect plot for S/N ratios

shown by Fig 4.7 for over cut . This graphs are represent the diameter of tool is directly

proportional to the over cut. Increasing in the discharge current from 1 to 3 A the OC is

decreasing, with increase in discharge current from 3A to 5A the OC increasing slightly.

Whereas, OC increases monotonically with the increase in pulse on time. Because which is

responsible for production of spark of tool and workpiece interface. it is given previous

researchers Jeswani [35]. And The interaction plot of OC is shown in Fig 4.8, where each plot

exhibits the interaction between three different machining parameters like Ip Ton and dia. of

tool. This implies that the effect of one factor is dependent upon another factor. It is also

confirmed by the ANOVA table (Table 4.8).



Page 52

Figure 4.7 Main effect plots for over cut

Figure 4.8 Interaction plot for over cut



Page 53

4.4.1 Model Analysis of OC

The coefficients of model S/N ratios for over cut shown in table 4.10 and parameter result

are standard deviation of error S=1.076, amount of variation R2 = 99.4% and R2 (adj.) = 97.6%.

And comparing the P value is less than or equal to 0.05 it can be concluded that the effect is

significant (shown in bold), otherwise not significant.

Table 4.10 Estimated Model Coefficients for SN ratios (OC)


Constant 6.12461 1.022 5.993 0.000

Dia 4 -3.94977 1.022 -3.865 0.005

Ip 1 6.19469 1.445 4.286 0.003

Ip 3 -2.94067 1.445 -2.035 0.076

Ton 50 -1.35038 1.445 -0.934 0.377

Ton 500 -0.07594 1.445 -0.053 0.959

Dia*Ip 4 1 -3.99804 0.3588 -11.144 0.000

Dia*Ip 4 3 2.28120 0.3588 6.358 0.003

Dia*Ton 4 50 -0.00677 0.3588 -0.019 0.986

Ip xTon 1 50 -1.89252 2.044 -0.926 0.382

Ip x Ton 1 500 -0.19081 2.044 -0.093 0.928

Ip x Ton 3 50 0.80375 2.044 -0.393 0.704

Ip xTon 3 500 -0.03116 2.044 -0.015 0.988

S = 1.076 R-Sq = 99.4% R-Sq = 97.6%

The residual plot for over cut is shown in fig 4.9. This residual plot in the graph for

normal probability plot indicates the data are normally distributed and variables are influencing

the response. And the Residuals versus fitted value indicate the variation is constant. And the

Histogram proved the data are not skewed and not outline exist. And Residual versus order of the

data indicates that there are systematic effects in the data due to time or data collection order.



Page 54


P e r c e n t

210-1-2

99

90

50

10

1

Fitted Value

S t a n d a r d i z e d R e s

i d u a l

20151050

2

1

0

-1

-2


F r e q u

e n c y

210-1-2

4

3

2

1

0

Observation Order

S t a n d a r d i z e

d R e s i d u a l

18161412108642

2

1

0

-1

-2



Residual Plots for over cut

Figure 4.9 Residual Plots for over cut

4.5

Conclusion

Experiments were conducted according to Taguchi method by using the machining set up

and the designed U-shaped tubular electrodes with internal flushing. Finding the result of MRR

discharge current is most influencing factor and then pulse duration time and the last is diameter

of the tool. In the case of Tool wear rate the most important factor is discharge current then

pulse on time and after that diameter of tool. In the case of over cut the most important factor of

discharge current then diameter of the tool and no effect on pulse on time



Page 55

Chapter 5

In the present study on the effect of machining responses are MRR, TWR and OC of the

AISI P20 plastic mould steel component using the U-Shaped cu tool with internal flushing

system tool have been investigated for EDM process. The experiments were conducted under

various parameters setting of Discharge Current (Ip), Pulse On-Time (Ton), and diameter of the

tool. L-18 OA based on Taguchi design was performed for Minitab software was used for

analysis the result and theses responses were partially validated experimentally.

(1). Finding the result of MRR discharge current is most influencing factor and then pulse

duration time and the last is diameter of the tool. MRR increased with the discharge current (Ip).

As the pulse duration extended, the MRR decreases monotonically

(2). In the case of Tool wear rate the most important factor is discharge current then pulse on

time and after that diameter of tool.

(3) In the case of over cut the most important factor of discharge current then diameter of the tool

and no effect on pulse on time .



Page 56

Chapter 6

Introduction –

In this chapter we are discuss about experimental used machine and equipment and which

propose are used.

Machine and Equipment

This Electrical discharge machine (EDM) was used to machine on for conducting theExperiments. This machine model ELECTRONICA- ELECTRAPULS PS 50ZNC (die-sinkingtype) with servo-head (constant gap).

Figure 5.1 Die Sinker EDM Model: PS 50ZNC



Page 57

Weighing machine

Precision balance was used to measure the weight of the workpiece and tool. This machinecapacity is 300 gram and accuracy is 0.001 gram and Brand: SHINKO DENSHI Co. LTD,

JAPAN, Model: DJ 300S.

Figure 5.2 Electronic Balance weight machine

Tool maker microscope This machine was used to measure the overcut which was occurs during EDM. This Tool

maker microscope Make : Carl Zeiss, Germany and Accuracy : 0.001 mm.

Figure 5.3 Tool maker microscope



Page 58

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[10] www.meetminitab.com

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